build: Support manually generating C# bindings via Github action and add a README (#423)

.github/workflows/test-csharp.yml

@@ -1,6 +1,7 @@
 name: bindings/csharp
 
 on:
+  workflow_dispatch:
   push:
     branches: [ "main" ]
   pull_request:
@@ -9,6 +10,9 @@ on:
     # Run at 8:00 AM every day
     - cron: "0 8 * * *"
 
+env:
+  VersionSuffix: ${{ github.event_name == 'workflow_dispatch' && 'manualtrigger' || null }}
+
 jobs:  
   build-ffi:
     name: 'Build Regorus FFI: (${{ matrix.runtime.target }})'